feat: make requirements.txt for extensions optional

There are multiple ways within python to declare dependencies (eg. via
pyproject.toml, setup.py or setup.cfg). Requiring a requirements.txt
file in a specific path doesn't work for a lot of projects out there
so make the requirements.txt file optional.

docs/reference/extensions/django-framework.rst

@@ -22,8 +22,8 @@ Project requirements
 
 There are 2 requirements to be able to use the ``django-framework`` extension:
 
-1. There must be a ``requirements.txt`` file in the root directory of the
-   project with ``Django`` declared as a dependency.
+1. ``Django`` needs to be declared as a requirement either in a `requirements.txt`
+   file or within another `pip` supported requirement (eg. via `pyproject.toml`).
 2. The project must be named the same as the ``name`` in ``rockcraft.yaml`` with
    any ``-`` replaced by ``_``, i.e., the ``manage.py`` must be located at
    ``./<Rock name with - replaced by _>/<Rock name with - replaced by _>/manage.py``

docs/reference/extensions/fastapi-framework.rst

@@ -19,8 +19,8 @@ Project requirements
 
 There are 2 requirements to be able to use the ``fastapi-framework`` extension:
 
-1. There must be a ``requirements.txt`` file in the root of the project with
-   ``fastapi`` declared as a dependency
+1. ``fastapi`` needs to be declared as a requirement either in a `requirements.txt`
+   file or within another `pip` supported requirement (eg. via `pyproject.toml`).
 2. The project must include a ASGI app in a variable called ``app`` in one of
    the following files relative to the project root (in order of priority):
 

docs/reference/extensions/flask-framework.rst

@@ -21,8 +21,8 @@ Project requirements
 
 There are 2 requirements to be able to use the ``flask-framework`` extension:
 
-1. There must be a ``requirements.txt`` file in the root of the project with
-   ``Flask`` declared as a dependency
+1. ``Flask`` needs to be declared as a requirement either in a `requirements.txt`
+   file or within another `pip` supported requirement (eg. via `pyproject.toml`).
 2. The project must include a WSGI app with the path ``app:app``. This means
    there must be an ``app.py`` file at the root of the project with the name
    of the Flask object is set to ``app``

rockcraft/extensions/fastapi.py

@@ -223,7 +223,7 @@ def _find_asgi_location(self) -> pathlib.Path:
 
     def _check_project(self) -> None:
         """Ensure this extension can apply to the current rockcraft project."""
-        error_messages = self._requirements_txt_error_messages()
+        error_messages = []
         if not self.yaml_data.get("services", {}).get("fastapi", {}).get("command"):
             error_messages += self._asgi_entrypoint_error_messages()
         if error_messages:
@@ -233,26 +233,6 @@ def _check_project(self) -> None:
                 logpath_report=False,
             )
 
-    def _requirements_txt_error_messages(self) -> list[str]:
-        """Ensure the requirements.txt file exists and has fastapi or starlette deps."""
-        requirements_file = self.project_root / "requirements.txt"
-        if not requirements_file.exists():
-            return [
-                "missing a requirements.txt file. The fastapi-framework extension requires this file with 'fastapi'/'starlette' specified as a dependency."
-            ]
-
-        requirements_lines = requirements_file.read_text(encoding="utf-8").splitlines()
-        if not any(
-            dep in line.lower()
-            for line in requirements_lines
-            for dep in ("fastapi", "starlette")
-        ):
-            return [
-                "missing fastapi or starlette package dependency in requirements.txt file."
-            ]
-
-        return []
-
     def _asgi_entrypoint_error_messages(self) -> list[str]:
         try:
             self._find_asgi_location()

rockcraft/extensions/gunicorn.py

@@ -77,7 +77,6 @@ def _gen_parts(self) -> dict:
                 "stage-packages": stage_packages,
                 "source": ".",
                 "python-packages": ["gunicorn"],
-                "python-requirements": ["requirements.txt"],
                 "build-environment": build_environment,
             },
             f"{self.framework}-framework/install-app": self.gen_install_app_part(),
@@ -95,6 +94,13 @@ def _gen_parts(self) -> dict:
                 "source": "https://github.com/prometheus/statsd_exporter.git",
             },
         }
+
+        # add the optional requirements.txt file
+        if (self.project_root / "requirements.txt").exists():
+            parts[f"{self.framework}-framework/dependencies"]["python-requirements"] = [
+                "requirements.txt"
+            ]
+
         if self.yaml_data["base"] == "bare":
             parts[f"{self.framework}-framework/runtime"] = {
                 "plugin": "nil",
@@ -259,24 +265,10 @@ def _wsgi_path_error_messages(self) -> list[str]:
 
         return []
 
-    def _requirements_txt_error_messages(self) -> list[str]:
-        """Ensure the requirements.txt file is correct."""
-        requirements_file = self.project_root / "requirements.txt"
-        if not requirements_file.exists():
-            return [
-                "missing a requirements.txt file. The flask-framework extension requires this file with 'flask' specified as a dependency."
-            ]
-
-        requirements_lines = requirements_file.read_text(encoding="utf-8").splitlines()
-        if not any(("flask" in line.lower() for line in requirements_lines)):
-            return ["missing flask package dependency in requirements.txt file."]
-
-        return []
-
     @override
     def check_project(self) -> None:
         """Ensure this extension can apply to the current rockcraft project."""
-        error_messages = self._requirements_txt_error_messages()
+        error_messages = []
         if not self.yaml_data.get("services", {}).get("flask", {}).get("command"):
             error_messages += self._wsgi_path_error_messages()
         if error_messages:
@@ -346,10 +338,5 @@ def _check_wsgi_path(self) -> None:
     @override
     def check_project(self) -> None:
         """Ensure this extension can apply to the current rockcraft project."""
-        if not (self.project_root / "requirements.txt").exists():
-            raise ExtensionError(
-                "missing requirements.txt file, django-framework extension "
-                "requires this file with Django specified as a dependency"
-            )
         if not self.yaml_data.get("services", {}).get("django", {}).get("command"):
             self._check_wsgi_path()

tests/unit/extensions/test_fastapi.py

@@ -178,25 +178,13 @@ def test_fastapi_missing_asgi_entrypoint(tmp_path, fastapi_input_yaml):
     assert "- missing ASGI entrypoint" in str(exc.value)
 
 
-@pytest.mark.usefixtures("fastapi_extension")
-def test_fastapi_missing_requirements_txt(tmp_path, fastapi_input_yaml):
-    (tmp_path / "app.py").write_text("app = app")
-    with pytest.raises(ExtensionError) as exc:
-        extensions.apply_extensions(tmp_path, fastapi_input_yaml)
-    assert str(exc.value) == (
-        "- missing a requirements.txt file. The fastapi-framework extension requires this file with 'fastapi'/'starlette' specified as a dependency."
-    )
-
-
 @pytest.mark.usefixtures("fastapi_extension")
 def test_fastapi_check_no_correct_requirement_and_no_asgi_entrypoint(
     tmp_path, fastapi_input_yaml
 ):
-    (tmp_path / "requirements.txt").write_text("oneproject")
     with pytest.raises(ExtensionError) as exc:
         extensions.apply_extensions(tmp_path, fastapi_input_yaml)
     assert str(exc.value) == (
-        "- missing fastapi or starlette package dependency in requirements.txt file.\n"
         "- missing ASGI entrypoint"
     )
 

tests/unit/extensions/test_gunicorn.py

@@ -308,41 +308,6 @@ def test_flask_extension_bare(tmp_path):
     }
 
 
-@pytest.mark.usefixtures("flask_extension")
-def test_flask_extension_no_requirements_txt_error(tmp_path):
-    (tmp_path / "app.py").write_text("app = object()")
-    flask_input_yaml = {
-        "extensions": ["flask-framework"],
-        "base": "bare",
-        "build-base": "[email protected]",
-        "platforms": {"amd64": {}},
-    }
-    with pytest.raises(ExtensionError) as exc:
-        extensions.apply_extensions(tmp_path, flask_input_yaml)
-    assert (
-        str(exc.value)
-        == "- missing a requirements.txt file. The flask-framework extension requires this file with 'flask' specified as a dependency."
-    )
-
-
-@pytest.mark.usefixtures("flask_extension")
-def test_flask_extension_requirements_txt_no_flask_error(tmp_path):
-    (tmp_path / "app.py").write_text("app = object()")
-    (tmp_path / "requirements.txt").write_text("")
-    flask_input_yaml = {
-        "extensions": ["flask-framework"],
-        "base": "bare",
-        "build-base": "[email protected]",
-        "platforms": {"amd64": {}},
-    }
-    with pytest.raises(ExtensionError) as exc:
-        extensions.apply_extensions(tmp_path, flask_input_yaml)
-
-    assert (
-        str(exc.value) == "- missing flask package dependency in requirements.txt file."
-    )
-
-
 @pytest.mark.usefixtures("flask_extension")
 def test_flask_extension_bad_app_py(tmp_path):
     bad_code = textwrap.dedent(
@@ -382,7 +347,6 @@ def test_flask_extension_no_requirements_txt_no_app_py_error(tmp_path):
     with pytest.raises(ExtensionError) as exc:
         extensions.apply_extensions(tmp_path, flask_input_yaml)
     assert str(exc.value) == (
-        "- missing a requirements.txt file. The flask-framework extension requires this file with 'flask' specified as a dependency.\n"
         "- flask application can not be imported from app:app, no app.py file found in the project root."
     )